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Old 25-12-2019, 20:49   #16
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Re: reverse osmosis / desalination

Rich will even help DIYers, cause he knows they will see reason one day anyway 8-)
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Old 26-12-2019, 11:44   #17
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Re: reverse osmosis / desalination

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Originally Posted by er9 View Post
interesting. i'm looking at a small portable katadyn for now but want to maybe play around with making a DIY RO unit at some point when I have the time. I thought I remember a thread on CF where someone was working on a DIY unit but cant seem to locate it.
The katadyn portable is an excellent unit to have in an emergency (like when you're cruising atolls in a dry spell) but are only good for drinking water as the filter replacement cost runs about a dollar per gallon so you won't be doing dishes, laundry or taking long hot showers with one of these.

That said Katadyn is the parent company of Spectra (pretty much the Cadillac of off shore cruising water makers). While these are apparently very reliable systems, at some point they will require service which may not be doable at sea, so having the back up unit makes perfect sense not just with a Spectra system but any other (possibly DIY) systems you might end up with.

For now, get the katadyn portable as it can always provide essential redundancy no matter what main system you arrive at. There are a good number of reverse osmosis builds on Facebook with guys building fairly robust systems for less than 2 grand (about a fifth of what a Spectra will set you back).
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Old 26-12-2019, 11:58   #18
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Re: reverse osmosis / desalination

I do not think you could build your own unit any cheaper than seawater Pro sells their basic kit for
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Old 26-12-2019, 13:36   #19
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Re: reverse osmosis / desalination

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Originally Posted by motion30 View Post
I do not think you could build your own unit any cheaper than seawater Pro sells their basic kit for
Looks like some of your post was cut short. https://seawaterpro.com/ Note that this unit is for 110v or 220v systems and won't work on 12v.
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Old 26-12-2019, 13:40   #20
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Re: reverse osmosis / desalination

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Originally Posted by joelhemington View Post
Looks like some of your post was cut short. https://seawaterpro.com/ Note that this unit is for 110v 0r 220v systems and won't work on 12v.

That is true. Basic Kit only works with 120v. If you purchase the upgraded pump you have the option of a 12volt motor. Not particularly energy efficient but I can run mine cuz I have. Large solar production
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Old 27-12-2019, 14:33   #21
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Re: reverse osmosis / desalination

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Originally Posted by sailcrazy View Post
I'll second the nod for CruiseRO watermakers. All the stuff is off-the-shelf (NOT manufacturer-specific), support is great, and the system works! You assemble and install, so you know the system, and can repair/tweek it as required. Ours is a 2015 30gph, and today produces 36-38gph!
yeah but they are $5k. That's kind of what has me looking into making my own. Im sure they are worth every penny though...Unfortunately im not so wealthy. The SeaWater Pro units though are more in my price range. I had never come across their product before. I would actually consider buying one of theirs at that price instead of trying to make one for $1500 give or take.
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Old 27-12-2019, 14:39   #22
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Re: reverse osmosis / desalination

Quote:
Originally Posted by joelhemington View Post
The katadyn portable is an excellent unit to have in an emergency (like when you're cruising atolls in a dry spell) but are only good for drinking water as the filter replacement cost runs about a dollar per gallon so you won't be doing dishes, laundry or taking long hot showers with one of these.

That said Katadyn is the parent company of Spectra (pretty much the Cadillac of off shore cruising water makers). While these are apparently very reliable systems, at some point they will require service which may not be doable at sea, so having the back up unit makes perfect sense not just with a Spectra system but any other (possibly DIY) systems you might end up with.

For now, get the katadyn portable as it can always provide essential redundancy no matter what main system you arrive at. There are a good number of reverse osmosis builds on Facebook with guys building fairly robust systems for less than 2 grand (about a fifth of what a Spectra will set you back).
Hey much thanks. good info. I was thinking something similar. get the katadyn for now as a basic survival unit in an emergency. it will eventually end up in the ditch bag when I have the time or can afford a built in unit.
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Old 27-12-2019, 14:46   #23
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Re: reverse osmosis / desalination

er9....In a former life, we raised and bred horses, on a small scale. And there was a saying......if you want good, clean oats-you must expect to pay a fair price. But...it if you can stand oats that have been thru the horse once....they come a little cheaper! You get what you pay for....they may be cheaper for a reason.
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Old 27-12-2019, 15:18   #24
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Re: reverse osmosis / desalination

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Originally Posted by sailcrazy View Post
er9....In a former life, we raised and bred horses, on a small scale. And there was a saying......if you want good, clean oats-you must expect to pay a fair price. But...it if you can stand oats that have been thru the horse once....they come a little cheaper! You get what you pay for....they may be cheaper for a reason.
lol...thanks for the humor. its something I really need to spend a lot more time researching before I make any decisions. fortunately its not something I need in a hurry and have plenty of time to do..
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Old 10-01-2020, 13:33   #25
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Re: reverse osmosis / desalination

If you DIY or use one of the cheaper kits that uses power washer pumps, you need to always have a spare pump on hand. And you need to flush the pump out with fresh water after running it. And you will want a spare pair of membranes. Those in the know generally use two membranes. There is a lot of engineering involved and you need to think about how you will monitor and regulate pressure at pump discharge, overboard brine discharge, flushing, etc, and how you will perform the backflush. Lots of valves there.



If you use your diesel occasionally, that is a perfect time to make water. Most sailboats are way overpowered anyway, so power to spare for loading the engine down a bit with a pump. Don't even think about a standard vee belt setup. Go with a serpentine belt upgrade. If you have a diesel genset of over 5kw or so, you might add the watermaker pump to it. You will want a clutch, be it manual, or solenoid. A two element setup should give you plenty of fresh water, running it just a couple of hours a week.



Possibly the best low budget option is buying used, when someone else upgrades. Most of these will be single element systems, many will have power washer pumps, but for some reason the PO will have found it wanting, which is why he is upgrading and trying to get a few hundred bucks out of selling the old system. Good way to get your foot in the door. When you upgrade, which is likely sooner or later, sell the old system for pretty much what you paid for it. It has already depreciated about as far as it can go, if it has worn out a pump. Hey you got a spare pump, right? So it is actually worth more than when you bought it. Somebody will love to have your hand me down watermaker.
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Old 10-01-2020, 15:32   #26
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Re: reverse osmosis / desalination

From NZ. We have been cruising offshore for fourteen years wth a spectra and nothing but trouble. Three pressure pumps and feed pumps and finally the intesnifier died so rebuilt my using only one feed pump(was using two)and the membrain plus the two three way taps.and the prefilters Then I used a power washer. ( $ 100 1200watts was the cheapest I could find. Remember we are on 240 volts) added a pressure gauge and a stop cockn the overboard line after the pressure gauge fitted by the high pressure hose people. Starting from scratch I know I could build one for $ 1000 in the States in would be much cheaper with no freightto NZ. Not only that I am producing 80 litres per hour against the Spectra which should have 30 litres but could not only get 20 litres and The Spectra agents could not get any more. I am using the same membrain now for about fifteen years and still perfect. PM me and I can draw up a plan and of instructions
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Old 10-01-2020, 17:55   #27
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Re: reverse osmosis / desalination

ECHOTec of Trinidad is a good source for a 50 litre/hr unit. Our 12 volt unit runs well
A friend built a similar one himself and told me that he saved little
Ours is a simple system. No electronics or regen pump
Start-up and shutdown take a minute or so, but we have no complex controls to go wrong
I am a mechanical engineer by profession. I could build my own, but have enough experience to know that the first one would involve some expensive learning by trial and error
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Old 11-01-2020, 12:46   #28
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Re: reverse osmosis / desalination

If you want cheap salt water to fresh water, simply use exhaust gas to heat salt water to steam and condense the steam. I know of a fellow who put an air cooled exhaust pipe straight up from his engine and it vented above the cockpit. He had a water-cooled manifold with a keel cooler. The exhaust was very hot. He built a tall, slotted stainless steel pot that fit around the exhaust pipe tightly, bailed salt water into it, clamped down the lid with pressure simple spring clamps (no real pressure in the pot even when it was boiling), and the steam was run through a long coil of copper tubing in a bucket. The weird looking device had no moving parts but would put off a gallon of very pure water every 30 minutes when the engine was running at power. The only thing I did not like about it was that it took up cockpit space and it might burn you. It was shielded with what looked like the exhaust shield on a truck but that got pretty hot.
I never trusted the reverse osmosis path because of its mechanical complexity and the fact that it typically leaves greater than 300 mg of NaCl per liter in the so-called "fresh" water it makes. That is a lot of salt if you drink a gallon a day. Rain catchers usually provide enough fresh water on a long voyage. But a water maker is a nice backup.
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Old 11-01-2020, 13:38   #29
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Re: reverse osmosis / desalination

Many commercial fishermen used evaporator desalination with their dry exhaust before RO was cheaper. If anyone builds one, the best way is with a diaphragm pump that can reach a vacuum. The pump collects the distilled water and pumps it to your tank. Under vacuum, the water in the evaporator boils at a lower temp. One issue is the evaporator needs to have the salt cleaned out often, otherwise it insulates the piping and requires more heat or makes less water.
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Old 15-01-2020, 01:19   #30
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Re: reverse osmosis / desalination

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Originally Posted by tkeithlu View Post
The pumps used in a RO unit are basically the same as used in pressure washers. Then you need a motor to run it, and 12v DC motors that strong are expensive. Then you need a membrane filter, which ain't cheap, then you need a way to flush the brine between sending loads of fresh salt water through the membrane, then you need a set of solenoid water valves, then you need a timing circuit to control all that, then you....

If you want to engineer your own as a very expensive DIY project, go for it, but don't expect to ever finish the job.
Well no.

No need for an electric motor. Just hook a belt onto your diesel engine.

The membrane is just a few hundred dollars, and you need a pressure vessel to put it in.

No need for timers and solenoids. Just open a valve by hand to flush fresh water in.

Standard household filters for incoming raw water is fine.

There is no need to have expensive UV treatment after.

But never flush the membrane with chlorinated water.

Maybe about $650 total spend.

Hint look for a big boat owner and ask if they happen to have a spare pressure vessel. I had two old ones I was not using and gave one away.
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